No Game Load (Sega Mega-Tech)
After you get game title data displaying on the Menu, you still may not get game load output on the Mega Drive AV Out (CN8).
To test if it is an AV output issue on the Mega Drive side or more of a Mega Drive fault, press the Test button. The Test button only works if you have at least one Game in the Menu.
If the Menu displays TEST MODE, check the Mega Drive AV out on CN8. It should show the test menu.
If the Mega Drive outputs the Test menu you can confirm your Mega Drive 315-xxxx logic chips, the AV chips and Z80 are all 100% working.
The only possibly issues left are:
- Dirty game slots of faults in the higher address pins of the cartridges or data/address ICs that interface to the slots (above the 68k).
- Dead 68k (test with a Master System game to rule this out as even needed)
- Bad traces to the Z80 and other 315-xxxx or data/address bus chips
The best test is to use a Master System game as it doesn't use:
- 68k processor
- Higher address pins over A16
Monitor that the Z80 comes out of reset after header load and stays out. If so, check the Master System Game Load section for further details on what is meant to happen.
The following pins are not needed to show the game title, but are needed to load the game, so are worth paying special attention to:
- 315-5313 Data pins D4 to D6 (would show corrupt title text however if bad)
- Z80 Data pins D4 to D6 (would show corrupt title text however if bad)
- 315-5313 Address pins over and including A6 onwards
The first reset is controlled by the SMS BIOS bringing the Mega Drive 68k/Z80 out of reset. After this the Mega Drive controls the reset and should attempt to bring it out of reset while reading in the entire game to load.
If it fails it will stay low. If it works, or even partly loads the reset pin should come back out of reset.
Here is Golden Axe failing to load (short pulse high after initial reset).
And here is Super Real Basket Ball which fails to load but keeps the console out of reset.
So failed loads can show both reset styles but usually you should still see at least a brief attempt at coming out of reset.
